In CFB reactors or combustors, reacting and non-reacting solids are entrained within a reactor enclosure by an upward gas flow which carries the solids to an exit at an upper portion of the reactor enclosure. There, the solids are typically collected by an impact type primary particle separator, and returned to a bottom portion of the reactor enclosure either directly or through one or more conduits. The impact type primary particle separator at the reactor enclosure exit typically collects from 90% to 97% of the circulating solids. If required by the process, an additional solids collector may be installed downstream of the impact type primary particle separator to collect additional solids for eventual return to the reactor enclosure.
As disclosed in U.S. Pat. No. 5,343,830 to Alexander et al., the use of impact type particle separators in CFB reactors or combustors is well known. To the extent necessary to describe the general operation of CFB reactors and combustors, the reader is referred to U.S. Pat. No. 5,343,830 to Alexander et al., the text of which is hereby incorporated by reference as though fully set forth herein. In one of the earliest CFB designs, an external, impact type primary particle separator having a plurality of impingement members arranged in staggered rows was used in combination with a non-mechanical L-valve and a secondary (multiclone) particle separator. The rows of staggered impingement members discharged all of their collected solids into a storage hopper located underneath them, and these collected solids were returned to the bottom portion of the reactor enclosure via the L-valve.
Later CFB designs employed additional rows of staggered impingement members which were positioned upstream (with respect to a direction of flue gas and solids flow through the apparatus) of the impingement members associated with the storage hopper and its L-valve. As disclosed in U.S. Pat. No. 4,992,085 to Belin et al., the text of which is hereby incorporated by reference as though fully set forth herein, a plurality of such impingement members are located within an upper portion of the reactor enclosure, arranged in at least two staggered rows. The impingement members hang and extend vertically across a width of the reactor exit, with collected solids falling unobstructed and unchanneled underneath these collecting impingement members along a rear enclosure wall of the CFB reactor or combustor. An important element of these "in-furnace" collecting impingement members, or "in-furnace U-beams" as they are generally referred to, is a baffle plate near a lower end of these impingement members which enhances their collection efficiency.
As disclosed in the aforementioned Alexander et al. '830 patent, CFB reactors or combustors are known wherein the two or more rows of impingement members located within the furnace or reactor enclosure are followed by a second array of staggered impingement members which further separate particles from the gas stream, and return them via cavity means and particle return means without external and internal recycle conduits.
It is apparent that a CFB reactor or combustor comprising an even more simple construction would be less costly and would be welcomed by industry.